The present invention relates to disc brakes for use on automotive vehicles.
A known disc brake for a motor vehicle typically includes a pair of in board and outboard brake shoes or pad assemblies placed on opposite sides of a rotor rotatable with a wheel to be braked and slideably supported on a carrier secured to a non-rotatable part of the vehicle. When a brake pedal is depressed, a caliper is moved on the carrier to urge the in board and outboard pad assemblies into frictional engagement with opposite sides of the rotor so as to apply the necessary clamping force thereto.
A problem associated with such a conventional disc brake is the frequent occurrence of a low frequency noise or squeal when the pad assemblies are pressed against the rotor. Such a noise is obviously uncomfortable to the driver. There is thus a need to substantially reduce the number of occurrences of such a low frequency noise.
An attempt has been made to reinforce the most deformed part of a carrier to increase its rigidity, as disclosed in Japanese laid-open patent publication No. 7-259901. This attempt is effective in reducing the extent of vibrations, but fails to reduce the number of occurrences of a low frequency noise (see FIG. 7).
Through an extensive search, the inventor has found that the occurrence of a low frequency noise of, for example, 1.8 kHz, is more closely related to vibrations of a carrier than to any other part of a disc brake. The carrier has various modes of vibration such as bending and torsion modes of vibration. The carrier typically includes a pair of inner arms located on the in board side of a rotor and having a pair of guides along which an in board brake pad assembly is axially moved, a pair of outer arms located on the outboard side of the rotor and having a pair of guides through which an outboard brake pad assembly is axially moved, an inner beam extending between the two inner arms and secured to a knuckle or other fixed part of a vehicle, and an outer beam extending between the two outer arms. In the torsion mode, the inner arms are twisted in opposite directions. This is also the case with the outer arms. In the bending mode, the inner and outer arms are bent about an axis parallel to the axis of the rotor. It has been found that these two different modes of vibration interact to cause a self-exited vibration and thus, a low frequency squeal.
In the disc brake shown in Japanese laid-open patent publication No. 7-259901, the difference in natural frequency between the bending and torsion modes is even less than that of the typical carrier known in the art (see FIG. 7). It is believed that an increase in rigidity of the carrier does not bring about a reduction in the number of occurrences of the low frequency noise.
Accordingly, it is an object of the present invention to provide a disc brake which enables a substantial reduction in the number of occurrences of a low frequency noise or squeal without the need for additional parts and without increasing its production cost and weight.